Method for producing a target

ABSTRACT

A target is produced inexpensively by safely incorporating an additive which is inflammable in the atmosphere. A primary alloy in a molten state is formed by adding an additive into a principal material in a low-level oxygen atmosphere, and a secondary alloy is produced by increasing the volume of the primary alloy through adding the principal material to the molten primary alloy in the atmospheric atmosphere. Since the primary alloys in the molten or solid condition are stable, it does not ignite in the atmosphere. Since the volume of the primary alloy is smaller than that of the secondary alloy, a smaller size of a vacuum chamber  11  for the formation of the first atmosphere suffices.

The present invention is a Continuation of International Application No.PCT/JP2006/304048 filed Mar. 3, 2006, which claims priority to JapanPatent Document No. 2005-66721, filed on Mar. 10, 2005. The entiredisclosures of the prior applications are hereby incorporated byreference herein in their entireties.

BACKGROUND

The present invention generally relates to a technical field on thesputtering targets; and more particularly, the invention relates to thetechnology for producing the targets in which an additive is added intoa principal material such as aluminum or the like.

In some cases, thin films for wiring or reflective films are formed byusing an Al or Al alloy target.

In a conventional thin film obtained by using the Al target, when thetemperature rises during annealing the thin film, Al undergoes graingrowth to produce a foreign matter called “a hillock” on a surface ofAl. When a wiring film is formed by etching the thin film having thishillock, the shaped patterns of the wiring film are disturbed.Meanwhile, when the reflective film is formed, light diffusely reflectsand the film becomes clouded and exhibits a low reflectivity becauseforeign matters are present on the surface of the thin film.

In order to avoid the above-mentioned hillocks, there is an Al alloytarget in which an additive is added into Al. However, since an additiveis dispersed as solid solution into Al in the case of an Al alloy target(such as, Al—Cu), the specific resistance of the formed thin film of theAl alloy becomes higher as compared to that of the Al thin film.

If the content of the additive is decreased in order to lower thespecific resistance, hillocks are formed; and whereas, if the content isincreased, the specific resistance becomes greater.

On the other hand, in the case of films of alloys (such as, Al—Nd or thelike), annealing can be performed at a high temperature while theproduction of hillocks is suppressed, and the specific resistance can bereduced by the annealing. With growth in sizes of substrates, however,targets become greater so that power applied to a cathode increases andarc discharge is likely to occur. When the arc discharge occurs, thereis a problem in that the target is partially melted and a splash isformed to mix into the thin film. A target in which an additive composedof a rare earth element is added into a principal material made of Al isdescribed in, for example, JPA 2001-073124.

When the additive (such as, a rare earth element) is incorporated bymelting, the additive is likely to react with oxygen in the atmosphereand ignites under heating because the additive capable of suppressingthe occurrence of the hillocks is active. For this reason, there is aproblem in that the conventional equipment for producing the targetthrough melting becomes large-scaled.

SUMMARY OF THE INVENTION

The present invention solves the problems and drawbacks in theproduction of the targets in the conventional art by incorporating theadditive into the principal material by melting, and provides a methodfor producing a target-constituting material without using a large-scalevacuum chamber.

In order to solve the above problems of the conventional art, thepresent invention is directed to a method for producing a target,wherein this method includes preparing a primary alloy in a molten stateby adding an additive into a principal material in a first atmosphere,adding the principal material to the primary alloy in a secondaryatmosphere to obtain a secondary alloy in a molten state, having acontent ratio of the additive lower than that of the primary alloy, andproducing a sputtering target composed of the secondary alloy, andwherein a partial pressure of oxygen in the first atmosphere is lowerthan a partial pressure of oxygen in the secondary atmosphere.

Further, the present invention is the target producing method in whichthe secondary atmosphere is an atmospheric atmosphere.

Furthermore, the present invention is the target producing method inwhich the pressure of the first atmosphere is lower than that of theatmospheric atmosphere.

Moreover, the present invention is the target producing method in whichaluminum (Al) is used as the principal material.

In addition, the present invention is the target producing method inwhich an inflammable metal that ignites if it is melted in theatmosphere is used as the additive.

Further, the present invention is the target producing method in whichat least one material selected from the group consisting of Ce, Pr, Dyand Y is used as the additive and the additive is incorporated into thesputtering target in the range of 0.5 atm % or more to 5 atm % or less.

Furthermore, the present invention is the target producing method inwhich a partial pressure of oxygen in the first atmosphere is 0.2 Pa orless.

Moreover, the present invention is the target producing method in whichthe first atmosphere is set at a pressure of 130 Pa or more.

In addition, the present invention is the target producing method toform the first atmosphere in a vacuum chamber and to add the additiveinto the principal material inside the vacuum chamber; and the targetproducing method further includes reducing the interior of the vacuumchamber to set to a pressure of 1 Pa or less; and an inert gas isintroduced into the vacuum chamber to set the pressure of 130 Pa or moreso as to form the first atmosphere.

The present invention is constructed as mentioned above, and theadditive which ignites by heating in the atmosphere, is melted in thefirst atmosphere with low-level oxygen; and the molten principalmaterial is mixed with the principal material in the molten state;thereby, forming the primary alloy. It may be that the molten additiveis added into the molten principal material; as such, the solid additivemay be alternatively added to the molten principal material to melt theadditive, or to the contrary, the solid principal material is addedlittle by little into the molten additive to melt the principalmaterial.

The molten primary alloy may be converted to a solid by cooling in thefirst atmosphere, or may be cooled after being taken out to theatmosphere, since the primary alloy is stable in the atmosphere even ifit contains the additive at a high concentration.

Since the primary alloy does not ignite even if it is melted in theatmosphere, the secondary alloy can be formed by increasing the volumeof the primary alloy by adding the principal material to the moltenprimary alloy in the atmosphere Therefore, since a large amount of thesecondary alloy can be obtained from a small amount of the primary alloyin the atmosphere, the vacuum chamber in which the first atmosphere isformed for the primary alloy can be made smaller than in a case wherethe additive and the principal material are all melted in a vacuumchamber.

The secondary alloy obtained is a target material. When the secondaryalloy is formed in a desired shape (such as, a rectangular plate-likeshape, a circular disc shape or the like), a sputtering target isobtained. The sputtering target may be attached to a backing plate ofcopper.

When the additive is melted into the principal material, the partialpressure of oxygen may be theoretically so high that the additive or theprincipal material may not be oxidized. The present inventorsexperimentally confirmed that no ignition occurs if the partial pressureof oxygen in the first atmosphere is set at 0.2 Pa or less when theadditive is Ce. It is anticipated that the same condition can be appliedto other materials (Pr, Dy or Y).

If the first atmosphere is constituted by an inert gas atmospherecontaining no oxygen, the pressure of the first atmosphere may be theatmospheric pressure. However, it is preferable that the interior of thevacuum chamber is evacuated to vacuum so as to remove a gas generatedfrom the melted principal material or the melted additive. For thispurpose, it is easy to set the first atmosphere at the pressure lowerthan the atmospheric pressure.

On the other hand, if the first atmosphere is set at a too low apressure, a vapor of the principal material or the additive is generatedfrom the molten principal material or the melted additive, it makes thecomposition of the primary alloy unstable.

Therefore, it is desirable that the first atmosphere is set at less thanthe atmospheric pressure and higher than a lower limit pressure.

Experiments revealed that the first atmosphere is preferably at thepressure of not less than 130 Pa, and that the pressure of the firstatmosphere is set preferably at not less than 2600 Pa so as to suppressthe generation of vapors of aluminum as the principal material and Ce asthe additive and to keep the compositional ratio of the first metalconstant.

For this purpose, after oxygen is removed by once vacuum evacuating theinterior of the vacuum chamber to a low pressure, it is preferable toform the first atmosphere consisting of the inert gas atmosphere at 130Pa or more, or not less than 2600 Pa by introducing the inert gas intothe vacuum chamber in order to raise its pressure.

Furthermore, in order to maintain the inert gas atmosphere free fromoxygen at less than the atmospheric pressure, it is preferable tocontinuously perform the vacuum evacuation and the feeding of the inertgas during the formation of the primary alloy.

According to the present invention, since the inflammable additive isadded at the low level-oxygen atmosphere (such as, the vacuum atmosphereor the inert gas atmosphere) having the pressure lower than theatmospheric pressure, there is no fear of ignition.

At that time, after forming the primary alloy in the low level-oxygenatmosphere, the volume of the primary alloy is increased by adding theprincipal material in the atmospheric pressure. Consequently, a greatamount of the target material can be obtained without using alarge-scale vacuum chamber.

Furthermore, when the target produced by the present invention issputtered, no abnormal discharge occurs, and no foreign matter is mixedinto a resulting thin film.

In addition, even when the thin film obtained is annealed, defects suchas hillocks, whiskers or the like are not developed. Therefore, thesputtering targets, which are suitable for the formation of reflectivefilms as well as of thin films to constitute electrode-wiring materialsfor electronic devices and apparatuses (such as, liquid crystaldisplays, etc.) can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for illustrating a step for producing a primary alloy.

FIG. 2 is a view for illustrating a step for producing a secondaryalloy.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The method for producing the sputtering target according to the presentinvention will be explained.

In FIG. 1, a reference numeral 10 denotes a first melting apparatus,which has a vacuum chamber 11.

A first melting crucible 12 is arranged inside the vacuum chamber 11.Meanwhile, an inert gas introducing system 15 and a vacuum evacuatingsystem 17 are connected to the vacuum chamber 11.

First, a principal material (herein, aluminum: Al) and an additive(herein, cerium: Ce) are placed inside the first melting crucible 12 ata predetermined ratio; and the interior of the vacuum chamber 11 isevacuated to vacuum at a pressure of not more than 1 Pa by means of thevacuum evacuation system 17.

Then, an inert gas (herein, argon gas) is introduced into the interiorof the vacuum chamber 11 through the inert gas introducing system 15;and the interior of the vacuum chamber 11 is pressurized up to 2600 Pa;thereby, forming a first atmosphere which has a lower pressure and alower oxygen pressure than the open atmosphere.

While the vacuum evacuation and the introduction of the inert gas arecontinuously performed and the first atmosphere having a lower pressureand a lower oxygen pressure than the atmosphere is being maintained, theprincipal material and the additive inside the first melting crucible 12are melted under heating by applying current to a high-frequencyinduction heating coil 14; thereby, obtaining a primary alloy 13 in amolten state.

Next, the molten primary alloy 13 is poured, in an inclined manner, intoa mold 16 arranged inside the vacuum chamber 11; thereby, obtaining theprimary alloy (a primary alloy ingot) 18 in a solid condition. In thisembodiment, the molten primary alloy is poured, in an inclined manner,into the mold 16 in the first atmosphere.

A metal (such as, Ce or the like), which is very active in theatmosphere, easily ignites under heating in the atmosphere. A metallicmass of Ce ignites at 160° C. in the atmosphere. However, Ce isstabilized through being alloyed with Al, and the primary alloy 18 doesnot ignite even if taken out to the atmosphere in a molten or solidcondition. Further, even if the primary alloy 18 is melted by heating inthe atmosphere, it does not ignite.

In FIG. 2, a reference numeral 20 denotes a secondary melting apparatushaving a secondary melting crucible 21. This secondary melting crucible21 is placed in a secondary atmosphere composed of the atmosphericcomponents at the atmospheric pressure.

The primary alloy 18 in the solid condition is placed in the secondarymelting crucible 21; a principal material is further added at a givenratio; and the primary alloy 18 and the principal material are melted inthe secondary atmosphere by generating heat to applying current to theheater 29; thereby, obtaining a secondary alloy 22 in a molten state.Since the principal material is further added into the primary alloy 18,the ratio of the additive to the principal material in the secondaryalloy 22 is lower than the ratio of the additive to the principalmaterial in the primary alloy 13, 18. The amount of the principalmaterial added is set such that the additive may be contained at adesired ratio in the secondary alloy 22.

After a contaminant is removed through a filter 23, the secondary alloy22 in the molten state is poured, in an inclined manner, into awater-cooled mold 24, and a secondary alloy (a secondary alloy ingot) isobtained in a solid condition by a continuously casting apparatus 26.

The microstructure of the solid secondary alloy is uniformized byplastic working, and a sputtering target having a given size is obtainedby mechanical working such as cutting.

A thin-film sample is formed by sputtering a target obtained from thesecondary alloy composed of Al as the principal material and Ce as theadditive.

With respect to the target in which the additive is added in a range of1 atm % or more and 10 atm % or less, the resistance value is reduced byannealing the resulting thin film.

In the present invention, the principal material is not limited to Al,but widely encompasses Cu, other metals and meltable materials.

The invention method is suitable for the case where the additive, whichignites at a low temperature in the atmosphere and thus cannot be meltedin the atmosphere, is added.

The additive is not limited to Ce, and rare earth elements (such as, Y,Pr, Dy or the like) are suitable for the target as the additive toprevent the hillocks.

Although argon is used as the inert gas in the above method, inert gases(such as, nitrogen gas) besides the rare gases (such as, argon) can bewidely used as the inert gas for the formation of the low level-oxygenatmosphere.

Although the pressure-reduced atmosphere of 2600 Pa was used as thefirst atmosphere in the above embodiment, the first atmosphere is notlimited to the pressure-reduced atmosphere. Any low level-oxygenatmosphere may suffice as long as the additive does not ignite therein.The inert gas may not necessarily be introduced.

According to the method of the present invention, targets are producedby using Al as the principal material and any one kind of the rare earthelements of Ce, Y, Pr and Dy as an additive; and thereafter, thin filmsare formed. With the above-described method, the following results wereachieved. With respect to the target having not more than 5 atm % of theadditive, the resistance values of the thin films were not more than 5μΩcm, which were sufficiently low and equivalent to 3 μΩcm in the caseof a thin film formed by an aluminum target. Further, the alloy in which5 atm % of Ce was added to Al had abnormal discharging smaller than inthe case of an alloy in which the same amount of Nd was added.Furthermore, the alloys, in which 5 atm % of any one kind of thematerials of Ce, Y, Pr and Dy is added less, suffered from theoccurrence of foreign matters as compared with those in which more than5 atm % thereof was added. In addition, when reflective films areformed, it was seen, different from the Al film, that the reflectance(λ=550 nm) does not decrease even when the films were annealed at 350°C. so that diffuse reflection owing to the occurrence of foreign matters(such as, hillocks) are suppressed.

Therefore, it is preferable to add any one or more kinds of thematerials of Ce, Y, Pr and Dy in the range of 1 atm % or more to 5 atm %or less when the Al alloy is produced, for the purpose of decreasing theresistance and suppressing the occurrence of the foreign matters onannealing.

1. A method for producing a target, comprising the steps of: preparing aprimary alloy in a molten state by adding an additive into a principalmaterial in a first atmosphere; adding the principal material to theprimary alloy in a secondary atmosphere to obtain a secondary alloy in amolten state having a content ratio of the additive lower than that ofthe primary alloy; and producing a sputtering target made of thesecondary alloy, wherein a partial pressure of oxygen in the firstatmosphere is lower than a partial pressure of oxygen in the secondaryatmosphere.
 2. The target producing method according to claim 1, whereinthe secondary atmosphere is the atmospheric atmosphere.
 3. The targetproducing method according to claim 2, wherein the pressure of the firstatmosphere is lower than that of the atmospheric atmosphere.
 4. Thetarget producing method according to claim 1, wherein aluminum (Al) isused as the principal material.
 5. The target producing method accordingto claim 1, wherein an inflammable metal that ignites if it is melted inthe atmosphere is used as the additive.
 6. The target producing methodaccording to claim 1, wherein: at least one material selected from thegroup consisting of Ce, Pr, Dy and Y is used as the additive, and theadditive is incorporated into the sputtering target in the range of from0.5 atm % or more to 5 atm % or less.
 7. The target producing methodaccording to claim 1, wherein a partial pressure of oxygen in the firstatmosphere is set at a pressure of 0.2 Pa or less.
 8. The targetproducing method according to claim 7, wherein the first atmosphere isset at a pressure of 130 Pa or more.
 9. The target producing methodaccording to claim 1 to form the first atmosphere in a vacuum chamberand adding the additive into the principal material inside the vacuumchamber, the target producing method further comprising the steps of;reducing the interior pressure of the vacuum chamber to set a pressureof 1 Pa or less, and then, introducing an inert gas into the vacuumchamber to set the pressure of 130 Pa or more so as to form the firstatmosphere.